The Justice Department charged Collins, 68, with securities fraud and lying to the FBI about his efforts to tip off family members with nonpublic stock information to help them avoid hundreds of thousands of dollars in investment losses.

Collins’s case centers on Innate Immunotherapeutics, an Australia-based bio-pharmaceutical firm that had been developing a drug to treat advanced multiple sclerosis. But when clinical trials showed the drug didn’t work, Collins — at the time firm’s largest shareholder and a board member — called his son, Cameron, and told him to sell off the stock before the news was made public, prosecutors alleged in the indictment.

Cameron Collins, 25, and his future father-in-law, Stephen Zarsky, 66, were charged with insider trading and lying to federal investigators.

All three pleaded not guilty.

Collins, who was also the first member of Congress to endorse Trump for president in 2016, made the announcement Saturday after initially pledging to run for reelection on Wednesday.

“I will mount a vigorous defense in court to clear my name," Collins said. "I look forward to being fully vindicated and exonerated.”

While Ryan and his GOP leadership team did not publicly call for Collins to step down, GOP sources said there was a “behind-the-scenes” effort in both Washington and New York to convince the defiant congressman that resignation was the best thing for the party three months before the crucial midterm elections.

In the days since Collins’s indictment and arrest Wednesday, there were a flurry of text messages and phone calls between Republican lawmakers, Capitol Hill aides, strategists and lobbyists concerned that the Collins corruption case could put his seat at risk and harm other vulnerable Republicans on the ballot, GOP sources said.

Some of these Republicans in Washington had been urging New York Republicans to personally appeal to Collins to resign, the sources said, making the case to him that he’s in an “untenable position.”

“No one is above the law, but Chris deserves his day in court and we will wait to see what unfolds,” said New York GOP Chairman Ed Cox.

But one former Collins supporter, David Gunner, the highway superintendent of East Aurora in Collins’s district, circulated a public letter to his fellow New York Republicans on Friday calling on the former Erie County executive to quit Congress.

“I believe Collins has done good things for Erie County and our Congressional District. Many times, he’s made us proud. But this insider trading scandal has put our district in real peril,” Gunner wrote. “If he runs, I don’t think he can win. I don’t care how much money he has, he can’t buy this seat — the good people of NY27 won’t stand for it.”

In his open letter, Gunner argued that if Collins continued to remain on the Nov. 6 ballot, he would be a drag on GOP candidates down ballot, including state Assemblyman Ray Walter and local office holders. Nationally, the Collins controversy could cause Republicans to lose control of the House majority, Gunner said.

The charges against Collins’s son were considered important leverage to convincing the congressman to relinquish his seat, said one New York Republican source. Collins could strike a deal with prosecutors, offering to plead guilty in exchange for his son and Zarsky avoiding jail time.

“A natural conversation between the U.S. attorney and Collins’s attorneys is to go easy on the son and father-in-law if Collins resigns,” the New York source said. “I’m sure that’s a conversation that is going on right now.”

A spokesman for Collins’s attorneys at Baker Hostetler did not return a call for comment prior to his Saturday announcement.

Collins’s situation is reminiscent of former Rep. Michael Grimm, another New York Republican who in 2014 was charged by the Justice Department with 20 counts of tax evasion. Grimm, a brash New Yorker like Collins, fought the charges, ran for reelection that year and won.

But that December, Grimm struck a deal with prosecutors, pleaded guilty to felony tax evasion and resigned his Staten Island congressional seat. He served seven months in prison.

In an interview with The New York Times, Grimm said Collins is in for a rough ride, especially once he returns to Washington from the August recess. But he urged his former House colleague to just focus on the work.

“He’s going to have a really, really difficult emotional time,” Grimm told the Times. “And whether he knows it or not, a lot of Washington is going to look at him as a pariah."

“He should go right back to his job and remain professional,” he said.

“I recognize how serious the allegations are and how difficult this is for Chris and his family,” Reed told The Hill. “And they will have to make their own decision on how best to proceed.”

It is not clear what Republicans' next steps will be in Collins's district. Although he will suspend his campaign, he already won the GOP primary in his district and will likely remain on the ballot.

Jerry Goldfeder, a New York–based lawyer who specializes in election law, told The Hill earlier this week that New York candidates can typically be removed from the ballot only if they die, run for another office or move out of state.